Validation and evaluation of VapA-specific IgG and IgG subclass enzyme-linked immunosorbent assays (ELISAs) to identify foals with Rhodococcus equi pneumonia.

The research article explores the effectiveness of VapA-specific ELISA for evaluating IgG and its subclasses (IgGa, IgGb, and IgG(T)) in the early diagnosis of pneumonia in foals caused by Rhodococcus equi. The article concludes that IgG(T) exhibits high specificity and sensitivity, marking a potential breakthrough in detecting and treating this type of pneumonia in foals.

Objective and Methodology

• The study’s objective was to evaluate the efficiency of a special type of ELISA (Enzyme-Linked Immunosorbent Assay), dedicated to VapA-specific (virulence-associated protein A) IgG (Immunoglobulin G) and its subclasses, in diagnosing pneumonia in foals triggered by Rhodococcus equi – a common bacterium causing foal pneumonia.
• The research involved validation of ELISA and assessment of diagnostic performance using samples from animals with confirmed health status. To do this, the researchers used serum samples from exposed and nonexposed adult horses, as well as from experimentally challenged and naturally infected foals.
• The scientists also conducted a historical review of post-mortem and tissue culture records from the Institute for Experimental Pathology at the University of Iceland in Keldur, Iceland, which indicated an absence of R. equi cases in the country.

Results and Evaluation

• Results showed that the VapA-specific IgG ELISA successfully differentiated exposed from nonexposed horses when using samples from Iceland, where no R. equi infection was reported.
• When identifying infected foals, VapA-specific IgG, IgGa, and IgGb did not have any diagnostic value. However, IgG(T) showed high sensitivity and specificity, indicating its potential as a reliable diagnostic tool.
• For each IgG assay, a cut-off value was chosen based on receiver operating characteristic curve analysis, which was then used to determine sensitivity and specificity. The researchers also calculated the intra- and interassay coefficients of variation for each ELISA.

Conclusions

• The findings suggest that horses from Iceland, which have not been exposed to VapA(+) R. equi, make suitable negative controls for this type of research.
• Except for IgG(T), VapA-specific IgG subclasses had poor predictive value in diagnosing the disease.
• Further investigation is needed on how IgG(T) can be effectively utilized as a diagnostic tool in practical field conditions.